First step is Make the spice rub. Place the brown sugar, mustard, paprika, garlic powder, onion powder, smoked salt, black pepper, and cayenne in a small bowl and stir to combine; set aside.

And then, Remove the membrane from the ribs. For super-tender ribs, remove the membrane that covers the bone on the underside of the ribs: Flip the ribs over so they're meat-side down, then slide a butter knife in between the ribs and the thin membrane of the first rack — start in the center of the rack, which tends to be easier than the ends. Once you’ve got a few inches pulled up, use your hands to gently pull the membrane up and completely off the bones (if your grip is slippery, grasp the membrane with a paper towel before pulling) off completely. Repeat for the remaining rack.

And then, visit for full instruction : https://www.thekitchn.com/instant-pot-ribs-recipe-258375?